1972 Evinrude 25HP Sportster Idle/Low Speed Problem

[CMelander]

This forum has been a treasure trove so far, but I am at a point where I haven't been able to find anything easily here regarding this issue.

I recently acquired a 1972 Evinrude 25 HP Sportster, model number 25202R. I have replaced the impeller, pulled the cylinder head and exhaust manifold to clean out a bunch of mud dauber crap from the water passages, replaced both coils, both condensers, both sets of points, spark plugs, fuel pump, and torn down and rebuilt the carb on it.

At this stage, she will run at high RPM, or according to the indicator on the tiller at 'high', but if I attempt to drop the throttle back to 'Start' or 'Shift', the engine dies. I have twiddled with the slow speed needle valve, and got it to where it would run smooth and nearly smokeless....but it still will die when I throttle down to anything much below 'High'.

I am waiting for the service manual for this particular motor, but I am impatient - want to get it out on the water and catch some fish. Is there something I am missing or not thinking about that would cause the engine to run smoothly at and above 'high' but die when I try to throttle back to get it in gear? Also, it cannot be started in the 'start' setting, it has to be started at 'high', choked as normal when cold.

Please help! Been working on it for a month plus now!

 

[oldboat1]

Well, little adjustment tab on float arm points down when you have the top inverted (i.e., when assembling the float). Float should be parallel with the edge of the inverted top, maybe slightly raised on the outside end. Use the wire clip if the float needle has the black tip. The nozzle gasket has to be in place. The high speed jet under the screw plug (bottom of bowl) has to be squeaky clean, likewise the idle passage up at the top. To get at the idle passages, you have to pull off the domed cap on top, replacing it with the one in the kit.

I soak the tops and bottoms after disassembly, then spray with carb cleaner (using plastic wand).

Needle adjustment is about 1 turn out from seated, maybe a little more. Start and warm up the motor, then adjust for best idle -- have to do that with some back pressure.

If the needle adjustment isn't sensitive, something was likely missed in the cleaning or assembly.

(This assumes spark is measured at around 3/8 inch or more, compression is even and around 100 to 125, give or take. Point gap is .020, Champion J4C plug gap is .030.)

 

[CMelander]

Needle adjustment is sensitive - engines revs change with adjustment, and the amount of smoking while running changes with adjustment. The only thing you mentioned above that I did not do was pull off the dome cap to get a direct route to the idle passage, but I soaked all of these and blew them out with carb cleaner using the plastic nextension.

Someone just told me that I may have linkage synchronization screwed up, but without the book I won't know for sure.

I will remove the carb again and just soak the entire body (minus gaskets) in carb cleaner overnight and also remove the dome cap so I can blast out the idle passage more directly.

 

[lindy46]

Synchronization is fairly easy. Adjust the cam follower roller so that the linkage to the carburetor just starts to open the carb butterfly when the roller hits the mark on the cam. There are two bolts on the underside of the cam for adjustment. Just loosen the bolts and move the cam in or out until you achieve the adjustment.

When you clean the idle circuit, make sure the orifice where the slow speed needle rides is not chipped or broken. That can cause idle problems.

 

[CMelander]

Ok, so before I pulled the carb off for a third cleaning D) I decided to twiddle with the throttle assembly.

All of it.

I adjusted a set screw at the back of the tiller - the screw is a standoff from the body of the motor, prevents the throttle from going too far and allows me to set where the roller on the cam rests when the throttle is cranked low. I piddled about with that for a bit, then reset the low-speed needle to 1 1/2 turns out from seated, and since I am a hillbilly and don't have nice things like muffs or a barrel, took it to the old river channel boat launch nd set it in the water.

It was a bear. I had to readjust the low speed needle several times; it would die and then not start until I made the idle mixture too rich again, then have to start all over. It was finicky as hell, but ultimately I was able to set it and get it to idle for 20 minutes in neutral without stalling.

Then I put it in gear.

Initially it died, and I had to repeat the above process. Turns out I need to open the throttle a little to get the revs up before engaging the prop, but the next problem I am dealing with is slipping out of gear as soon as any throttle is applied.

The idle and all of that I can fine tune once I get the manual but I want to get it to where I can go on the lake and at least test drive it without fear of being stuck out there and having to paddle in.

My plan is to access the inspection port and adjust the clutch linkage so that I can get a solid forward gear engagement - right now, it will slip out of forward or reverse easily, but I believe I can correct one gear or the other with adjustments, and worry about opening the lower unit and replacing worn parts (if I can find them) later.

Thoughts?

 

[racerone]

Sorry----There is NO adjustment at that oval port on the side of the exhaust housing.---Adjustment is at the shift lever up top !

 

[CMelander]

As I discovered!

I will keep you posted on developments, have to wait out some storms before I can resume. Also that grind of 9 to 5 ...

 

[CMelander]

Ok, so solved the gear issue (set screw was loose) and run into a new problem.

I have little power. When engaged, I am getting maybe a third of the thrust I should be getting. Engine revs don't seem to significantly increase when throttling up, either. WOT get me about 7 or so mph, on a 16 foot stripped down aluminum hull.

Where should I look next? Totally at a loss. It runs, just purely horrible...

 

[AlTn]

with the engine in fwd gear advance the throttle to wot...as you advance the throttle is the cam follower rising to the highest point on the timing cam?...at this point is the throttle butterfly exactly horizontal in the carb throat?..the engine does not need to be running to check these. If the timing cam is not moving as you twist the throttle to wot, check that the "key" at the bottom of the vertical shaft is intact and both "ears" of the key are in place. If all this is good, take a timing light out and observe the flash with it hooked up to each plug wire. Both plug wire flashes consistent in brightness and consistency? If so, look to the fuel side.